1. Field of the Invention
The present invention relates to a system and method for controlling a multi-cylinder internal combustion engine operable in a variable displacement mode to reduce the time required for a catalyst to reach a desired operating efficiency.
2. Background Art
Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine such that it is sometimes referred to as a variable displacement engine. Mechanisms which reduce the effective stroke of one or more cylinders may also be used to provide a variable displacement mode of operation. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light load conditions, for example. In some engine configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively activated and deactivated.
Reducing the effective displacement by reducing the number of operating cylinders may also reduce the operating temperature of various engine and/or vehicle components which may adversely affect desired engine control or operation. For example, emission control devices, such as catalytic converters, and associated exhaust gas oxygen (EGO) sensors require a minimum operating temperature to function as desired. In the case of some EGO sensors, a reliable indication of oxygen content (or air/fuel ratio) which may be used for more efficient closed loop control of the engine requires a minimum operating temperature. Likewise, emission control devices having catalysts require a minimum operating temperature for efficient operation. For variable displacement engines configured to selectively operate an entire bank of cylinders, sensors and catalysts associated with the deactivated bank may cool below the desired operating temperature. Likewise, emission control devices and related sensors require some period of time after a cold start to operate efficiently. It is desirable to minimize the time required for these components to reach associated desired operating temperatures after starting the engine.
An object of the present invention is to provide a system and method for controlling an engine operable in a variable displacement mode during and shortly after starting to reduce the time necessary for emission control devices and related sensors to reach a desired minimum operating temperature. Another object of the present invention is to reduce or eliminate the time required to achieve a desired minimum operating temperature for components associated with one or more deactivated cylinders operating in a variable displacement mode.
In carrying out the above objects and other objects, advantages, and features of the invention, a system and method for controlling an internal combustion engine having at least one bank of cylinders operable in a variable displacement mode include starting the engine with at least one bank of cylinders deactivated to increase load on at least one other bank of activated cylinders and reduce time required for an engine and/or vehicle component to reach a desired operating temperature. In one embodiment, ignition timing or spark is retarded and air/fuel ratio is operated lean for the activated cylinder bank during and shortly after starting to further reduce the time required for catalyst light off and closed loop operation. During activation of a deactivated bank of cylinders, air/fuel ratio of one or more activated cylinders is biased rich with air/fuel ratio of the deactivated cylinders biased lean. In addition, spark is retarded during activation of the deactivated cylinders to reduce the time necessary for components associated with the deactivated cylinders to reach desired operating temperatures.
The present invention provides a number of advantages. For example, the present invention controls the engine during and shortly after starting to reduce the time necessary for emission control devices to reach a desired operating efficiency. Furthermore, the present invention, reduces the time after starting or activating a deactivated bank of cylinders to operate in the more efficient closed loop mode.
The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.